The principles of the present invention can be used in connection with any injector requiring high level pressurization of the fluid to be injected. High pressures may be needed for expelling high viscosity product, such as products in oil, gelled, paste, amorphous or suspension form, e.g. for dental purposes or to form slow release deposits in the body. Another major injector type requiring high pressure is jet injectors for needle-less skin penetration of a pressurized liquid to be further discussed below. Although for convenience the invention will be described in terms of such jet injection, the invention shall not be regarded as restricted thereto but shall be understood to embrace other high pressure applications as well.
Jet injection apparatuses for hypodermic jet injection of medical liquids through the skin surface or the mucous membrane of either humans or animals under sufficiently high pressure to force the liquids to a predetermined depth within the tissue beneath the skin surface are known in the art since many years.
A multi-shot injector instrument employing the jet injection principle is known from U.S. Pat. No. 2,821,981. In this known instrument the fluid to be injected is charged into a distal pressure chamber, an ampoule, from a proximal fluid medicine chamber, e.g. in the form of a conventional syringe. One mechanism is used to transfer the fluid from the fluid chamber into the pressure chamber and another mechanism is then used to perform the injection. Non return valves are provided in the transfer bore to ensure that no back flow occurs. The mechanically rather complicated structure of the injector instrument makes it rather expensive to manufacture. Another drawback with this type of complicated mechanical instruments is the difficulty to assemble the device in a sterile environment. It is sometimes today a demand to make parts non-reusable (disposable) that might be contaminated during injection. This demand is very difficult to fulfil for a device of the type disclosed in U.S. Pat. No. 2,821,981, or generally for mechanically complicated devices of this kind, due to the large number of different parts making up the device.
U.S. Pat. No. 3,138,257 discloses an injector device similar to the one of U.S. Pat. No. 2,821,981.
U.S. Pat. No. 4,447,225 discloses a multi-dose jet injector adapted to receive a medicament bottle or vial from which the medicament liquid is transferred into a transfer chamber. The medicament is then pumped through a one-way valve via a cannula to a medicament delivery chamber. The medicament is then ready for jet injection delivery, which is performed by imparting an ejecting force on the medicament liquid and thus expelling it through an orifice of the jet injector. One drawback with the jet injector disclosed in U.S. Pat. No. 4,447,225 is that it is structurally complicated, e.g. the two step transfer of the medicament liquid prior injection, and thus expensive to manufacture.
WO-92/01485 discloses a two-compartment syringe with a barrel, made e.g. from plastic, comprising a distal and a proximal section. An insert made from a material, e.g. glass, which is compatible with the solvent, or liquid medicament, is inserted, into the proximal section of the barrel. The solvent is transferred into the distal section, where the liquid solves a lyophilized powder, via a by-pass arrangement and the syringe is then ready to be used for an ordinary hypodermic needle injection. It should be observed that the syringe disclosed in WO-92/01485 is intended for traditional needle injection, i.e. there is no indications at all that the distal section could resist a higher pressure needed for high pressure injections, e.g. having front sealings and arrangements unable to sustain high pressures. The design is purely adapted for a lyophilisation step to take place in the front compartment.
U.S. Pat. No. 2,591,046 discloses a hypodermic syringe assembly with two chambers separated by a by-pass section. The liquid medicine is transferred into a distal chamber via the by-pass section. There are no separate chambers able to provide different properties, e.g. resistance against high pressures.
Liquid medicaments intended for injection are ordinarily stored in glass containers prior loaded into a syringe for injection. A rubber seal then seals the glass container. Thus, the liquid medicament is only in direct contact with glass and rubber. The major reason for not using plastic materials as material for medical storage containers is that the plastic material does not provide an entirely closed sealing with regard to oxygen moving into or components out from the container. Also components from the manufacture might be deposed in the plastic material that can affect liquid stored in the container. Another reason is that plastic material may give off trace amounts of components that are unacceptable in injectable preparations. The above mentioned drawbacks regarding plastic material used for medical storage containers are valid only when using plastic containers for normal medical storage times, e.g. up to 2 years. When using plastic materials in e.g. syringes etc. where the liquid medicine only contacts the plastic material when the injection is to be performed the above mention drawbacks can not be identified.
In jet injectors using glass containers, the class container must resist the high pressure used to expel the liquid from the container. The glass container is then preferably manufactured from hardened glass, which renders it expensive. On the contrary, plastic materials can easily provide the necessary properties for a pressure chamber, such as strength and resilience with low shattering risks. Glass materials for storage chambers and plastic materials for pressure chambers are also suitable for disposable single-use components.
The object of the present invention is to achieve an easy to use injector device that is less expensive to manufacture than those known from the prior art. Another object of the present invention is to achieve a device not having the above-mentioned drawbacks regarding the sterile handling of parts of the device. A further object is to offer an injector device suitable to be pre-filled with medical and allowing storage over extended periods of time before injection and wherein all surfaces of the device and its parts being or coming into contact with the medical can be kept sterile during manufacture, storage and use. Still another object of the present invention is to achieve a device provided with sterile parts that inherently cannot be reused in order to prevent unauthorized sterilization and reselling of already used devices that might be dangerous to patients.